Display screen or portion thereof with transitional graphical user interface



FIG. 1 is the first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing our new design;

FIG. 2 is the second image thereof;

FIG. 3 is the third image thereof;

FIG. 4 is the fourth image thereof;

FIG. 5 is the fifth image thereof; and,

FIG. 6 is the sixth image thereof.

The broken line showing of the text and the symbols within the figures forms no part of the claimed design. The outermost broken lines show a display screen or portion thereof and form no part of the claimed design.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-6. The process or period in which one image transitions to another image forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 